Current environmental preoccupations stress more and more the importance of the quality of the air we breath. It is widely acknowledged that industrial plants, such as those that synthesize chemical compounds or that burn fuels such as coal, produce a large amount of atmospheric pollution that is detrimental to the health of not only the workers at the immediate vicinity of the plant but also the residents of the neighbouring cities.
The Manager of the plant must therefore control the amount of such toxic wastes evacuated into ambient air.
A good analysis of composition of air pollutants found in North America a well as in the Soviet Union is found in a relevant article presented by an Officer of the U.S. government Environmental Protection Agency (EPA) in the August, 1987 edition of the rigorous "Scientific American" magazine. In one graph therein, a curve wa plotted with the X axis representing he diameters of the different particles found in the atmosphere of polluted areas of said regions and with the Y axis representing the relative number of the particles of any given diameter. By inspection, it can be found that the curve is bi-modal, (defining two peaks) with a high concentration of the particles in the air at about 0.1.mu. and also at about 10.mu. of diameter, Hence, the majority of the particles to be filtered in the air being of different diameters by an order of about 1 to 100, efficient filtering thereof would require more than a single type of filter means, since selective filtering must be used.
The capital costs of installing effective air pollution control implements are however extremely large, and these costs should not of course be such as to hamper the profitability of the business concern running the industrial plant. The problem is to know where to strike the line between the extent of purification of the exhaust smoke from the industrial plant, on one hand, and the capital expenditure required for said purification, on the other hand.
Several types of air-purifying devices have been suggested in the art: a good survey thereof is found in the
introductory pages of the Canadian Patent No. 1,060,778 issued Aug. 2, 1979 to Societe SACILOR, Acieries et Laminoirs de Lorraine (France). Since installation of such devices is not widespread, it is believed by the present inventor that improvements in this field are desirable.